We are running MongoDB (v 3.6.6) in replication mode (1 primary and 1 secondary) on two nodes (running Ubuntu 14.04.5 LTS,  64GB memory).
We experienced the following error on primary instance:

2018-12-26T19:22:24.491-0500 F -        [conn111] Invalid access at address: 0
2018-12-26T19:22:24.808-0500 F -        [conn111] Got signal: 11 (Segmentation fault).
 0x7ffc4cdb78b1 0x7ffc4cdb6ac9 0x7ffc4cdb7136 0x7ffc495b3330 0x7ffc4b790953 0x7ffc4b7910b5 0x7ffc4b7935e5 0x7ffc4b793edb 0x7ffc4b7922bd 0x7ffc4b795671 0x7ffc4c6a6e05 0x7ffc4cc6b5b4 0x7ffc495ab184 0x7ffc492d803d
----- BEGIN BACKTRACE -----

{"backtrace":[

{"b":"7FFC4AB64000","o":"22538B1","s":"_ZN5mongo15printStackTraceERSo"}

,{"b":"7FFC4AB64000","o":"2252AC9"},{"b":"7FFC4AB64000","o":"2253136"},{"b":"7FFC495A3000","o":"10330"},{"b":"7FFC4AB64000","o":"C2C953"},{"b":"7FFC4AB64000","o":"C2D0B5","s":"_ZN5mongo19ServiceStateMachine22_scheduleNextWithGuardENS0_11ThreadGuardENS_9transport15ServiceExecutor13ScheduleFlagsENS2_23ServiceExecutorTaskNameENS0_9OwnershipE"},{"b":"7FFC4AB64000","o":"C2F5E5","s":"_ZN5mongo19ServiceStateMachine15_sourceCallbackENS_6StatusE"},{"b":"7FFC4AB64000","o":"C2FEDB","s":"_ZN5mongo19ServiceStateMachine14_sourceMessageENS0_11ThreadGuardE"},{"b":"7FFC4AB64000","o":"C2E2BD","s":"_ZN5mongo19ServiceStateMachine15_runNextInGuardENS0_11ThreadGuardE"},{"b":"7FFC4AB64000","o":"C31671"},{"b":"7FFC4AB64000","o":"1B42E05"},{"b":"7FFC4AB64000","o":"21075B4"},{"b":"7FFC495A3000","o":"8184"},{"b":"7FFC491DA000","o":"FE03D","s":"clone"}],"processInfo":{ "mongodbVersion" : "3.6.6", "gitVersion" : "6405d65b1d6432e138b44c13085d0c2fe235d6bd", "compiledModules" : [], "uname" :

{ "sysname" : "Linux", "release" : "3.13.0-24-generic", "version" : "#47-Ubuntu SMP Fri May 2 23:30:00 UTC 2014", "machine" : "x86_64" }

, "somap" : [ { "b" : "7FFC4AB64000", "elfType" : 3, "buildId" : "F63278FD698B5843222FE7A6C8FF17D6AEFBBE38" }, { "b" : "7FFF52AFE000", "elfType" : 3, "buildId" : "6755FAD2CADACDF1667E5B57FF1EDFC28DD1C976" }, { "b" : "7FFC4A724000", "path" : "/lib/x86_64-linux-gnu/libresolv.so.2", "elfType" : 3, "buildId" : "AD304AFCE6847F7A4D66D22853E87CCBF5A66966" }, { "b" : "7FFC4A348000", "path" : "/lib/x86_64-linux-gnu/libcrypto.so.1.0.0", "elfType" : 3, "buildId" : "CE5EE930D4F0B1F47EDFDACC388EAC6C4DE5CDD2" }, { "b" : "7FFC4A0E9000", "path" : "/lib/x86_64-linux-gnu/libssl.so.1.0.0", "elfType" : 3, "buildId" : "920BD37B19B7BD04CA38CE35155D6CDCD744EAB5" }, { "b" : "7FFC49EE5000", "path" : "/lib/x86_64-linux-gnu/libdl.so.2", "elfType" : 3, "buildId" : "034D6A4EE9DCAB4A34ABD644345CBBB42DC63088" }, { "b" : "7FFC49CDD000", "path" : "/lib/x86_64-linux-gnu/librt.so.1", "elfType" : 3, "buildId" : "4F930712D3609C93E380E5BE5DF73E7AD273531C" }, { "b" : "7FFC499D7000", "path" : "/lib/x86_64-linux-gnu/libm.so.6", "elfType" : 3, "buildId" : "300C7884CDEB5667BEA2357D2B8E7A76397562D6" }, { "b" : "7FFC497C1000", "path" : "/lib/x86_64-linux-gnu/libgcc_s.so.1", "elfType" : 3, "buildId" : "36311B4457710AE5578C4BF00791DED7359DBB92" }, { "b" : "7FFC495A3000", "path" : "/lib/x86_64-linux-gnu/libpthread.so.0", "elfType" : 3, "buildId" : "F64B8AD471FBA1B7A3A64EFB01551E694975E1F7" }, { "b" : "7FFC491DA000", "path" : "/lib/x86_64-linux-gnu/libc.so.6", "elfType" : 3, "buildId" : "D9A10B8EF90300628DD0A3A535106967714D7328" }, { "b" : "7FFC4A93F000", "path" : "/lib64/ld-linux-x86-64.so.2", "elfType" : 3, "buildId" : "2CA513EDC89C7BC06EC183D1A3A03CC0F606319C" } ] }}
 mongod(_ZN5mongo15printStackTraceERSo+0x41) [0x7ffc4cdb78b1]
 mongod(+0x2252AC9) [0x7ffc4cdb6ac9]
 mongod(+0x2253136) [0x7ffc4cdb7136]
 libpthread.so.0(+0x10330) [0x7ffc495b3330]
 mongod(+0xC2C953) [0x7ffc4b790953]
 mongod(_ZN5mongo19ServiceStateMachine22_scheduleNextWithGuardENS0_11ThreadGuardENS_9transport15ServiceExecutor13ScheduleFlagsENS2_23ServiceExecutorTaskNameENS0_9OwnershipE+0x175) [0x7ffc4b7910b5]
 mongod(_ZN5mongo19ServiceStateMachine15_sourceCallbackENS_6StatusE+0xAF5) [0x7ffc4b7935e5]
 mongod(_ZN5mongo19ServiceStateMachine14_sourceMessageENS0_11ThreadGuardE+0x23B) [0x7ffc4b793edb]
 mongod(_ZN5mongo19ServiceStateMachine15_runNextInGuardENS0_11ThreadGuardE+0x11D) [0x7ffc4b7922bd]
 mongod(+0xC31671) [0x7ffc4b795671]
 mongod(+0x1B42E05) [0x7ffc4c6a6e05]
 mongod(+0x21075B4) [0x7ffc4cc6b5b4]
 libpthread.so.0(+0x8184) [0x7ffc495ab184]
 libc.so.6(clone+0x6D) [0x7ffc492d803d]
-----  END BACKTRACE  -----
 

NOTE: I am attaching the mongo diagnostic data